Regioselective Tandem [4 + 1]–[4 + 2] Synthesis of Amino-Substituted Dihydroxanthones and Xanthones
Ana Bornadiego, Jesús Díaz, Carlos F. Marcos.
Regioselective Tandem [4 + 1]–[4 + 2] Synthesis of Amino-Substituted Dihydroxanthones and Xanthones.
Journal of Organic Chemistry. May 2015.
A highly convergent and operationally simple approach to mycotoxin-related 4-amino-substituted 1-hydroxydihydroxanthones is described. The target compounds are obtained in one pot by the multicomponent reaction of 3-carbonylchromones, isocyanides, and nonsymmetric dienophiles. The reaction, which involves a tandem [4 + 1]–[4 + 2] cycloaddition, efficiently affords a variety of both monomeric and dimeric polysubstituted dihydroxanthones structurally similar to bioactive ergochromes. Further aromatization to the corresponding xanthones is readily achieved by treatment with DBU under microwave irradiation.